Cadastral Surveying - Data Capturing Techniques PDF

CHAPTER 3 Data Capturing Techniques  Data capture means entering information into the system.  Data acquisition are also referred to as data capture, data automation, data conversion, data transfer, and digitizing.  When acquiring data, one must bear in mind: purpose, scale, resoluti...

CHAPTER 3 Data Capturing Techniques  Data capture means entering information into the system.  Data acquisition are also referred to as data capture, data automation, data conversion, data transfer, and digitizing.  When acquiring data, one must bear in mind: purpose, scale, resolution, accuracy, completeness, content, costs, datum transformation and map projection.  A key success factor for any GIS or cadaster is acquisition of data appropriate for the identified applications.  Data acquisition traditionally is the most costly component of a GIS and Cadastral project. (approx. 80%)  Data availability and data quality requirements affect the time taken and cost incurred in database development. Data Capturing Techniques  Data sources for cadastral map preparation  Traditional Methods  Ground surveying  Total station  RTK GNSS (GPS)  Chain  Remote sensing  Satelite emegery  Arial photo  1. Traditional Methods  Traditional methods vary both between and within countries. They typically consist of a relatively simple method for measuring parcel boundaries and another for area estimation.  Common examples would be to use ‘Kada’, ‘Timad’ and the rope method which utilizes a rope of known length (e.g., 50 m, 100 m) to measure boundaries of parcels.  Areas are determined using simple mathematical methods (areas of rectangles and triangles) with assumptions on parcel shape.  Ground Surveying Methods 1. Measurement Tape With Compass The standard surveyor’s compass is a hand-held device which shows the bearing of a line relative to magnetic north. Reads bearing to 0.5°  Simple, quick and inexpensive  Calculation may be time consuming  High accuracy  Updating and maintenance surveys  Inaccuracy in length of tape, slope, temprarature, pressure, sag etc.  2. Theodolites  Optical/mechanical  Measures angle  Replaced with total stations  3. Total Stations  In the past, transit & theodolite were the most commonly used surveying instruments for making angle observation. These two devices were fundamentally equivalent and could accomplish basically the same task.  Today, the total station instruments have replaced transit and theodolites.  Total station can accomplish the entire task that could be done with transit and theodolite and do much more efficiently. A total station is a combination of theodolite and electronic distance measuring device (EDM).  electronic angle and distance measurement  built-in field computer to calculate positions  has millimetre level accuracy  demands line of sight to the objects, minimum of two known points  expensive  In addition, they can also observe distance accurately and quickly. Furthermore, they can make computation with angle and distance observation and display the resulting real time. They are used for all types of surveying include, topographic, hydrographic, cadastral and construction survey.  They combine three basic components;  1) Electronic distance measuring instruments (EDM.)  2) Electronic angle measurement instruments  3) Computers or microprocessor....into one integral unit  Total station do not use any signal from satellite to fix a position on the ground. Hence it has high advantages in urban and forest area than satellite methods.  Total station is very accurate instrument. For example Leica TPS1200+ model has a superb accuracy of 1 mm + 1.5 ppm for a range of 3 km. And it has a choice of accuracy for angle from 1 to 5 seconds.  Instrument Set Up  Instrument Set Up: Mount the instrument onto the tripod and secure firmly. Level and centre the instrument precisely to ensure the best performance. Use the tripod with a 5/8” tripod screw.  Operation Reference: Levelling and Centring the Instrument 1. Setting up the tripod: First extend the extension legs to suitable length and tighten the screws, firmly plant the tripod in the ground over the point of beginning. 2. Attaching the instrument to the tripod: Secure the instrument carefully on the tripod and slide the instrument by loosening the tripod mounting screw. If the optical plumb site is positioned over the centre of the point tighten the mounting screw. 3. Roughly levelling the instrument by using the circular vial: Turn the levelling screw A and B to move the bubble in the circular vial, in which case the bubble is located on a line perpendicular to a line running through the centres of the two levelling screw being adjusted. Turn the levelling screw C to move the bubble to the centre of the circular vial. Recheck the position of the instrument over the point and adjust if needed. 4. Levelling by using the plate vial: Rotate the instrument horizontally by loosening the Horizontal Clamp Screw and place the plate vial parallel with the line connecting levelling screws A and B, then bring the bubble to the centre of the plate vial by turning the levelling screws A and B. Rotate the instrument 90° (100g) around its vertical axis and turn the remaining levelling screw or levelling C to centre the bubble once more.  What does Total station does?  Can observe horizontal and vertical angles as well as slope distance from a single setup;  From these data, they instantaneously compute elevation and coordinates of points sighted and display the result;  Can store data  Averaging multiple angles and distance measurement  Calculating point elevation  Computing coordinates from horizontal angle and distance  Detail Measurement Traversing  4. Global Positioning System (GPS)  GPS is a satellite-based navigation system that was developed by the U.S. Department of Defense in the early 1970s.  Initially, GPS was developed as a military system to fulfill U.S. military needs.  GPS consists, nominally, of a constellation of 24 operational satellites.  To ensure continuous worldwide coverage, GPS satellites are arranged so that four satellites areplaced in each of six orbital planes.  4. Global Navigation Satellite System (GNSS)  Provides precise three dimensional position, navigation, and time information  Different GNSS  Global Positioning System (GPS) – America  GLONASS - Russia  GALILEO - European  Compass - China RTK GPS, can be used depending on the project requirements, location, and other factors. The RTK surveying, however, seems to be the most suitable method, especially in unobstructed areas. Inaccessible locations or obstructed areas can be surveyed with integrated systems such as GPS/total station.  GNSS receivers … 4.1 Handheld GPS Receive radio signals from GPS satellites Average accuracy 6m Inapplicable for cadastral surveying Useful for reconnaissance surveying, large investment area Navigation purpose  4.2 Precision GPS/RTK GPS  Two receivers (base and rover)  Receives radio signals but with advanced technique of measuring the phase of the radio waves  Few millimetre to cm accuracy  much easier and quicker than total station the combination of speed and accuracy makes it the most suitable tool for cadastral surveying  more expensive than total stations  inefficient under shades (building and trees)  Advantages of Precision/RTK GPS  Inter-visibility between the points is not required with GPS. This means that extensive traversing is eliminated, clear-cutting is not required, and intervening private properties is avoided.  GPS provides user-defined coordinates in a digital format, which can be easily exported to any GIS system for further analysis.  The accuracy obtained with GPS is consistent over the entire network; such accuracy is lacked by conventional surveying methods.  Also, with GPS, one reference station can support an unlimited number of rover receivers.  GPS Positioning  Point positioning: employs one GPS receiver that measures the code pseudo ranges to determine the user’s position instantaneously, as long as four or more satellites are visible at the receiver  Relative positioning: employs two GPS receivers simultaneously tracking the same satellites.  Remote Sensing Materials 1. Satellite Images  It is a convenient way of collecting cadastral data.  This is comparatively new technique that makes it possible to use georeferenced image and digitize features.  Nowadays, satellite images with a resolution of less than one meter are possible to obtain in Ethiopia. Geo-referencing will be done by software such as ArcGIS.  Using the tools of software, it is then possible to draw the whole parcels from details that are marked in the image.  Parcels drawn from images should therefore be regarded as a helpful tool to collect data, but should always be followed by a confirmation survey on the ground such as handheld GPS.  Spatial resolution  Spatial resolution of an imaging system can be measured in a number of different ways. It is the size of the smallest object that can be discriminated by the sensor.  The greater the sensor's resolution, the greater the data volume and smaller the area covered.  Ortho-rectification  Geo-referencing  Digitizing features on the image  Resolution (pixel size) 18:34 20  Advantage of Satellite Image  Generally, the image gives a very good overview of the survey, making it easy to verify that all parcels and details in an area are measured.  Making a parcel is easier in satellite image than with ground survey.  It is easy to detect in the image if e.g. a parcel border line is slightly bent, and digitize this with some extra points along the line.  This is often missed in ground surveys, where the bent border is often only represented by a single line.  Disadvantage of Satellite Images  The image is describing the landscape as it looked like when the image was taken. If e.g. two years have passed since then, landscape might have changed considerably by changed parcel shapes, new roads, etc.  Clouds might obscure parts of the image.  High initial cost  To georeferencing the image, it is needed to find details in the image that can be clearly identified in the field. This can sometimes be difficult, and there is a risk of mixing.  The accuracy depends on the ortho-rectification process  Cont.… Disadvantages  Digitized parcel borders between two parcels might be wrong for two reasons.  Firstly, two farmers might use the same crops, making the border invisible in the image.  Secondly, one farmer might grow two different crops on the same parcel, making one parcel look like two different parcels in the image.  Sources of errors  Errors in the geo-referencing  optical errors in the camera used  Errors in surveyed reference points  High precision GPS or total stations are recommended for the survey of the ground points for Georef.  In General, satellite images are excellent tool to acquire a general planning map, but confirmation in the field of each parcel is necessary.  It is also important to check the image accuracy regarding both the resolution and the orthorectification.  2. Aerial Images  Aerial photogrammetry involves the use of photographs taken in a systematic manner from air.  Aerial photography is the taking of photographs of the ground from an elevated position.  They are then controlled by land survey and measured by photogrammetric techniques.  It deals with the photographs taken by an aerial camera on board aircraft at different-altitude.  Accuracies achieved are comparable with those obtained by land survey and in many cases the work is carried out more economically.  Conti…  Aerial photos are one commonly used form of raster data, with only one purpose, to display a detailed image on a map or for the purposes of digitization.  Aerial photography may be classified according to its scale:- 1) Small scale aerial photography: which cover a large area but does not show detail data 2) Large scale aerial photography: which cover small area but shows great detail. Aerial photograph  Advantages of Aerial over Satellite Images  considerably lower height of exposures gives high resolution often on decimeter level in ground coordinate system.  From a stereo pair of images, a 3D model can be created from the stereo perspective of the details in the images. This will automatically give an accurate terrain model for the rectification.  The amount of needed ground control points is much lower than terrain model needed for satellite image rectification.  The use of ground control points for photogrammetric calculations will give an accurate georeference of images.  Therefore, an orthorectified aerial image is generally an accurate tool for cadastral digitizing.  The amount of needed ground control points is much lower than terrain model needed for satellite image rectification.  It may be made for places that are inaccessible to ground survey.  It provides the current pictorial view of the ground. Disadvantages of Aerial Images  Detail variation in terrain features aren't readily apparent without overlapping photography and stereoscopic viewing.  Recent aerial images of a given area are very expensive.  The method to capture the photograph is also expensive.  Comparison Results RTK GNSS HH GPS Orthophoto HRSI Accuracy in RMS (+m) 0 4.10 0.60 1.50 Labour (par/sur/day) 30 30 40 40 Cost per parcel ($) 12.5 7 8 10 Re-establishment possibility Excellent Poor/no V good Good Connection to a grid Yes no yes yes Multipurpose V good good Excellent Excellent Combination possibility yes yes yes yes Existing resources yes yes Going on no  Question for Discussition 1. Did you know one traditional method used in Ethiopia for measuring land? 2. Discuss the drawback of using traditional data capturing methods for cadastral surveying? 3. Discuss the advantages of using total station for data capturing in cadastral surveying? 4. What is the d/ce between Satellite and aerial Image? 5. Discuss the benefits of using satellite image for data capturing in cadastral surveying? 6. Can you write something about Global Positioning System? 7. Discuss the application of GPS for cadastral surveying? 8. Which data capturing methods is more appropriate and recommended for cadastral surveying? Put strong justification Methods Recommendation Combination of survey methods Mainly ortho-photo for establishment Mainly RTK GPs for maintenance 18:34 32 Cadastral surveying Process for Imajery/Orthophoto 18:34 33  Land Holder Preparations Boundaries  Land holders must ensure that the boundaries of their land are clearly marked on the ground. Registration  Registration will be in the names of those people who are in the existing legal documents. Therefore, these documents must be made available. Besides, the existing registration in ISLA will be used.  Demarcation  Landholders and neighbours must be present at their parcel when demarcation and adjudication/verification is taking place, so that he/she can show land boundaries to the Team Surveyors and Kebele Committee.  The absence of land holders is slowing down the process. Inform them in time through LA committee! 18:34 35  Demarcation continued...  Any documents held – including 1st level certificates (Green books) must be presented.  Attribute/text information will be recorded in the field on a field data sheet. A printout from ISLA with information about the parcel will be brought to the field to confirm or change the existing registered information.  The parcel boundaries will then be drawn on the image, first with pencil, later with pen. 18:34 36 The parcel is given a unique parcel number which will also be written on the image. Intervals are used to avoid overlaps. The structure used in Amhara is Region, Zone, Woreda, Kebele, Holding and Parcel ID (e.g. AM/EE/7/23/12/2). 18:34 37  Demarcation continued... Where the boundaries are not clear or are not shown on the image, landholders will assist the surveyors to measure the land using taped measurements from objects visible on the image, so that they can draw the boundaries of that land on the image. 18:34 38  Both agreed and disputed boundaries will be recorded on hard copy prints of the relevant image using a pencil (later with pen). The unique parcel ID is then written in the middle of the parcel. An overlap between the images exist. 18:34 39 18:34 40 Parcel map 18:34 41  THE END!! THANK YOU FOR YOUR ATTENTION!!